A. Related Applications
There are no applications related hereto heretofore filed in this or any foreign country.
B. Field of Invention
Our invention relates generally to ammonium nitrate-fuel oil (ANFO) blasting agents and more particularly to an additive for such agents that provides gelling materials, energy and sensitivity additives and dry fuels to form water impervious, explosive, peripheral gells upon water impingement.
C. Background and Prior Art
Ammonium nitrate explosive mixtures have been known since the time of Nobel, and since that time have evolved through various stages. Initially they were combined with primary explosives such as nitro-glycerin in dynamite formulations, where the ammonium nitrate served primarily as an active oxidizing agent. The ammonium nitrate used was a crystalline product of graining kettles. Such mixtures were known as ammonia dynamites and in these applications, the blasting strength of the mixture was about 70 percent of that of the contained nitro-glycerin. These ammonia dynamites had little water resistance but, because of their lower cost, lower velocities of detonation and higher gas yield, could be used in dry conditions, with both cost savings and blasting advantages. In the 1930's, the water resistance of such compositions was somewhat improved by the addition of cold water soluble gums, such as guar gum and locust bean gum.
After the Second World War, when porous ammonium nitrate prills first became available to industry from war surplus plants, it was soon discovered that the addition of dry or liquid carbonaceous fuels made the ammonium nitrate into an economical, safe and effective blasting agent. This class of blasting agent required dynamite to initiate detonation, as the material was not sensitive to a blasting cap like other explosives, and was inherently safer. The material has since become the most widely used explosive in modern day commerce. The explosive commonly is called "ANFO" and that term is herein used to refer to such compounds. The primary drawback of this material is that it has very little water resistance and is difficult or impossible to use in wet environs.
In practice ANFO is made by mixing about 6 percent of diesel fuel oil with about 94 percent of porous ammonium nitrate prill, to give substantial oxygen balance and optimum performance. This mixture of ANFO performs comparably to 50 percent gelatin dynamite in rock blasting. The low cost, higher gas yield, safety of storage and ease of loading, have all contributed to wide acceptance of this material in blasting. ANFO, however, is soluble to the extent of 118 gms/100 ml of water at 0 degrees C., to 871 gms/100 ml of water at 100 degrees C. This high solubility in water has prevented direct use of ANFO in wet drill hole conditions to this day, as even as little as 6 percent water by weight will cause an ANFO column to fail to detonate. Various methods of overcoming this deficiency have been tried over the years, such as the addition of guar flours and other water thickening products, higher viscosity oils and greases as fuels to coat the prills, encapsulation of the prills in waxes and the like, but largely with no particular degree of success or acceptance by explosive users. Perhaps the most successful water-proofing method heretofore developed has been "sleeving", wherein a drill hole is pumped free of water, a double polyethylene sleeve is placed in the hole, weighted down by a primer stick of dynamite, and loaded with ANFO before water can return in the hole. This method has found some degree of acceptance, but a tear in the plastic sleeve is a common hazard and often results in failed detonation.
Parallel to the development of ANFO, it was found that ammonium nitrate in a saturated aqueous solution, with the proper sensitizers, gel structure and density controllers, could be detonated satisfactorily in wet conditions. A sophisticated technology of slurries, water gels and emulsions developed around this finding. Slurries with explosive sensitizers were classed as explosives, and those with non-explosive sensitizers were classed as blasting agents. Sensitized aqueous ammonium nitrate compositions were invariably in the form of gels, with viscosity controlled to suit the use and at the same time maintaining a uniform and stable suspension of sensitizers. While free flowing dry ANFO compositions have a density of about 0.85 gms/cc, gelled slurries have densities in the range from 1.20 to 1.55 gms/cc, depending on formulation and amount of entrained air. The density of all slurries is heavier than water so they will sink in water filled holes. Most slurries, water gels and emulsions perform comparably in blasting to fully coupled ANFO columnar loads, on a volume for volume basis, and will out perform cartridged ANFO loads.
Because of the added weight required and higher (per pound) costs of slurries, considerable effort has been extended to develop methods to keep ANFO dry to allow its use in wet bore hole conditions. Polyethylene bags have been found marginally suitable for this, either in the form of individual cartridge bags with a tear resistant outer covering, or double walled bags with water proof seals. These later bags have been produced for example in 5 inch.times.30 pounds or 8 inch.times.50 pound sizes, and if a blasting composition used in them were not modified to obtain a sinking density, drill holes in which they were used had to be pumped free of water before lowering the cartridges. Even though these polyethylene bags were double walled, they had to be handled and loaded carefully because a minor puncture or tear would allow entry of water and might cause a bore hole to fail to propogate an explosion. Such bagged material when stacked in a drill hole needs multiple primers spaced up the column, and is never fully coupled to the walls of the drill hole, causing less than optimum performance. These cartridging methods, however, are still quite widely used with ANFO blasting agents in wet environs in 4 inch and larger diameter drill holes.
Slurries followed a parallel development in the use of plastic cartridges. Because of their inherent water resistance and density, however, they could be poured or pumped into water filled drill holes without a plastic liner or cartridges. In this way, as a slurry was pumped into a wet drill hole, being heavier than water, the water was displaced upwardly resulting in a drill hole loaded solid in its bottom part with product, similarly to ANFO poured into a dry hole. With both the cartridged ANFO and cartridged slurries, there is a significant increase in cost of both the product and priming, the former because of the added packaging costs, and the latter, because stacked cartridges require multiple primers to insure reliable detonation. A further disadvantage was that bore holes are not completely filled by the cartridges and there is therefore a significant loss of performance because of lack of complete explosive column coupling in a bore hole.
There is presently no intermediate alternative product between the economical dry, free flowing ANFO blasting agents and the more expensive slurries. Our present invention provides a new and novel composition that effectively fills this gap.